It is generally well known that inkjet printers are used for printing characters and/or images onto various substrates. Inkjet printers have print heads made up of individually addressable piezoelectric chambers, formed within a piezoelectric material. When actuated and de-actuated, the piezoelectric chambers eject ink droplets and suck in more ink into the chambers. These ink droplets may be placed on the surface of a substrate in a controlled manner, thereby forming individual characters and/or images on the surface of the substrate.
The piezoelectric chambers are controlled using a driver circuit, which is used to apply a predetermined voltage waveform to each of the chambers. The piezoelectric material acts a capacitive load and the capacitance is proportional to the number of piezoelectric chambers actuating at any one time. Therefore, the current required to actuate the chambers increases proportionally with the number of actuating chambers.
For accurate printing, it will be apparent that the drive voltage waveform should have very highly controlled rise and fall slew rates, being of the order of a few μsecs. The current waveform generally consists of a trapezoidal positive pulse during the rise time and a similar negative pulse during the fall time, with no current being drawn during the “on” time.
In most cases, the predetermined voltage level of the waveform, which may be a substantially constant voltage, is of the order of 20-30 V, but in some systems, may need to be a relatively high voltage, for example up to 150 V. In these cases, large power supplies may be needed to power commercial print heads. Of course, high power requirements and large power supplies mean that complex control circuitry and bulky heat dissipaters are required to ensure that heat is removed from the print head without causing damage to the surrounding printing system. This means that the current, of about 1.5 A, is only required for very short periods, even though the high voltage is required for the full “on” time.